Esterification of organic acids with separation of the esters in highly concenetrated form



May 21, 1935. TRK 2,001,926

y ESTERIFICATION OF ORGANIC ACIDS WITH SEPARATION OF THE ESTERS IN HIGHLY CONCENTRATED FORM Filed June 9, 1932 2 Sheets-Sheet 1 2,001,926 EsTERIFIcATIoN-OF ORGANIC AcIDs WITH SEPARATION Maly 2l, 1935- G. TRK

OF THE ESTERS IN HIGHLY CONCENTRATED FORM Filed June 9, 1932 2 Sheets-Sheet 2 M M lll!! f R N o y w M. f M M I|l| LEM 8 z m fm 4. Hf d y h .af LT `E my mIII mmm m5 4 s 4 (Ww C 8 I N 2 M, Imm m k IST g T s w E 5 ma m 9 9 CHN w Z, N 2 x 3 y 3 EW T A @4l um HEBT EXCHQNGEE Patented May 2l., 1935 ESTERTFICATION oF ORGANIC Aorns WITH SEPARATION or 4'rmi EsTERs TN HIGHLY ooNcEN'rRATEn FORM GraberA Trk,4 Budapest, Hungary Application June 9, 1932, Serial No. 616,314A

i In Germany JuneV 13, 1931 Y 5 claims. (ol. 26o-106) This invention relates to a process for the esteriiication of organic` acids with separation of the esters in highly concentrated form."

In the direct esterification of aqueous organic acids, as it is known, the alcohol is used in large excess. The separation of the alcohol-ester mixture thereby produced,with theproduction of highly concentrated esters, is, even in the case of the low boiling alcohols, only possible with some diiculty, ,inthe case of-working up higher boiling alcohols which are* only slightly soluble in water such as butyl or amyl alcohol however only a very incomplete separation can be effected.

The present process hasior its object thedirect conversion of aqueous organic acids intoI esters `with the production oi highly concentrated products v also 4 including the case of working up higher and more diflicultly water-solublaalcohols. Inr `this process 'the boiling point ofthe 4alcoholemployed at .any time, and of the ester lprepared therefrom must not attain to `100" C.; or; if falcoholszboiling above l"-.C., such as butyl alcohol, are employed, the-boilingpoint` of `the binary or ternary umixtures formed from such an alcohol and the corresponding ester or from either` orxboth with Water must not attain to In 'the process according to the inventionthe esterificationis carried out in two consecutive working stages which are effected in conjunction with one another but which ltake place separately, the'working conditions being selected so that in one phase the processjis carried out with an excess `of alcohol (excess alcoholV stager) but in theother there is an excess of acid (excess acid stage). The unconsumed acid from the excess facid stage is passedto the excess alcohol stage ,Where it is esteriied practically without residue. nThe portion of theexcess alcohol `therebyunconsumed is passed with the ester produced into the excess yacidstage and there likewise esteried practically without residue. This method of working allows of the application of `an excess Aof alcohol also including the case of the esterication of the above-mentioned higher boiling diilicultly water-soluble alcohols and, gives' in very incompletely by washing. Y

In the excess alcohol stage, in the known manner, the dilute organic acid (for example fermen- ,tation acetic acid) iiows with the application of sulphuric acid or the like through a column from top tobottom` `and is thereby esterifled `practically without residue by the alcohol vapours rising from the bottom'inexcess. The vapour mixture of alcohol-ester-water passing out 'at :the head of the column then passes to the excess acid stage; it is allowed to rise in a second column against the downwardly moving dilute organic acid; By this means the alcohol contained in the rising vapors is Vest'erilied practically without residue by the acid which is here passed'in in excess. The binary vapor mixture passing out from the head of'this'column consisting essentially only of ester and water now finally leaves the system and can. be condensed either immediately orafter traversing a small neutralization column which is charged with warm dilute sodium carbonate or` alkali metalacetate solution or the like The portionV of `excess'acid collecting in the lower part of thecolumn is employed for the supply of thecolumn working with excess of alcohol and soon.

t When water soluble alcohols 'are esterifed thenftherexcess" of alcohol `in the excess alcohol stage Ycan'be selectedof any suitable amount if care is taken that anytoo great excess of alcothrough this intermediate collun'n with a downward ilow of warm water, without difficulty a viapor' mixture can be lobtained with alcohol content reduced torany'desired extent or `with an ester. content of any desired value (up to aboutv 60-90%).L` iThe quantity and temperature of the wash water is fin this `connection regulated so that theltemperature of the water-alcohol solution produced on'the one `handrremains below its own boiling point and onthe other hand however exceeds the boiling point of the ester or of the binary ester-Water `or ternaryesterwater-alcohol mixture. The "vapor mixture leaving the intermediatecolumn is now passed into the excess acidvstagek the aqueous -alcohol iiowing downwards is however returned into the excess alcohol phase. U Y

As wash liquid forthe intermediate column instead of water any. suitable dilute salt solution can be employed or also .the dilute acid to be esteried itself; in' the latter'case from the wash liquid flowing down the alcohol is driven oi and Athe alcoholpassed to theesterification In the working up of difficulty Water soluble alcohols this intermediatecolumn is dispensed with. The excessA of alcohol should not exceed 100%. The ester-alcohol-water vapor mixture passing out of the column of the excess alcohol stage is passed immediately into the column of the excess acid stage where the preponderating portion of the entrained alcohol is likewise .esterified.

As catalysts are employed ythe hitherto used mineral acids, active column-filling materials of large surface or both.

The drawings illustrate diagrammatically lan embodiment of the apparatus to be used for carrying out the process. The drawings `will be' explained with reference to the following ex-` amples:

Example 1 I' From the container I2 (Fig. 1b) throughvth tube 2l methyl alcohol of about 95% is passed into the column I with simultaneous switching on of the heating devices I4, 35 and 35 (Fig. la). The vapors of the methyl alcohol pass through an ordinaryV dephlegmator, not shown, and through the tubes 28 and 30 with the valve 38 closed and the valver v39 open into the wash column 4 to which from the container l0 through the tube 23 lis led warm water at a temperature of about 40-50 C. The methyl alcohol vapors are condensed or dissolved by the Warm water and the aqueous solution is passed through the tube 3l and the open valve 4I) into the alcohol evaporator 2 Where the alcohol is again vaporised. The quantity of methyl alcohol, maintained in circulation in this manner and later constituting the permanent excess, which traverses Athe cross section of the column per unit time amounts .to about four times that quantity of methyl alcohol which is the equivalent to the quantity of acid to be introduced into the column per unit time. As soon as this quantity is attained there commences the controlled supply of the ,acid from the container 8. This acid is a,30-40% acetic acid which-is already mixed with sulphuric acid in such a proportion that thel acid mixture contains for 1 kg. of absolute acetic acid about 0.250.75 kg. of sulphuric acid of 50 l changer I3, through the tube 22 to the lcolumn f 3 and through the tube 25 to the column I and rattains by the tube 34 to the upper portion of the esterication column I at a temperature which y is higher than the boiling point Vo1 the methyl acetate. While the acid mixture'iiows downwards its acid content is converted into methyl acetate which with theexcess of methyl alcohol in the Vvapor form leaves the column I through the dephlegmator and thetube 28.A 'Ihe dilute y sulphuric acid already free from acetic acid passing to the alcohol levaporator 2 is here freed from alcohol and leaves the system through the tube32, heat exchanger I3 and Vtube 33. i The ester-alcohol vapor mixture passes through the tube 28 into the wash column 4. B y means of the warm water supplied from the container l the desired portion of the'excess Aof alcohol is washed out of the vapor mixture, the aqueous alcohol is passed back through the tube 3I into the alcohol evaporator 2 where as the vapor mixture consisting of methyl acetate and the residual methyl alcohol passes through the tube 24 into the esteriflcation column 3 where the methyl alcohol is likewise converted into ester by the excess of acid flowing from top to bottom. The acid mixture containing some alcohol collecting in the lower portion of the column 3 passes through the tube 25 into the column 'I and from here the alcohol is conducted through a dephlegmator not shown and through tube 25 into the lower part of the column I while the acid passes through the tube 34 into the upper part thereof. The methyl acetate vapors entraining some free acid passing out at the head of the column 3 through a" dephlegmator likewise not shown and through the tube ISI are washed in the neutralisation column 5 with l to 2% Warm potassium acetate solution from the container 9, pass through a'icurth dephlegmator not shown and throughthe tube l'I,`are condensed in the cooler 6 and recovered at The sulphuric acid can also ow immediately from the container I I into the column l in which case from the container 8 only the dilute acetic acid Ais supplied.

Example 2 Y 'Ihefcontainerv 8 contains amixture of 10% acetic acid and sulphur-ic acid, about 10-30 kg. of 'sulpliuric acid of 501B. being calculated per 100 kg'. of 19% acetic acid. The container I2 contains 96% ethyl alcohol. The quantity of the excess of alcohol maintained in circulation amounts to about @-8 times, and the quantity continuously added about 1.1 to 1.3 times the calculated equivalent quantity. The temperature of the wash water for the intermediate column 4 and also that of the dilute potassium acetate solution for the neutralization column 5 is maintained at about 'l5-80 C. Otherwise the course of the `process corresponds'exactly to that according to Example 1. f

The'container 8 is lled with a mixture of 10% acetic acid and sulphuric acid as in Example 2. The container I2 contains 98% n-butyl alcohol which forms in the column system at 92 C. a

binary vapor mixture of 57% butyl alcohol and 43% water. The excess of butyl alcohol is not retained in circulation but instead per unit time so much butyl alcohol is introduced into the column l as amounts to about 1.5 to twice that yquantity of butyl alcohol which is equivalent to the acetic acidsupplie'd to column I per unit time. The vapor mixture of butyl acetate-butyl alcohol-water passing out at the head of the column I at a temperature of 8992 C. passes through the dephlegmator not shown and the tubes v28, 23, 24 immediately into the esterification kcolumn 3, where, under the action of the acetic acid which is there present in excess, the

preponderating portion of its butyl alcohol con- Various changes may be made in the details described in the foregoing specification without departing from the invention or sacricing the advantages thereof.

I claimzfl 1. A process for the direct conversion of watersoluble lower fatty acids with monohydric aliphatic alcohols into highly concentrated esters which are practically free from alcohols, in which the esterication of the aqueous lower fatty acid is effected in two consecutive, conjoint, but separately proceeding working stages, in the rst stage with an excess of alcohol and in the second stage with an excess of acid, practicallyV completely esterifying the said fatty acid by subjecting the liquid acid coming from the excess acid stage to the action of excessive quantities of alcohol vapors led in counter-current to it, and practically completely removing any alcohol vapors from the ester by subjecting the ester vapors re- .sulting from the excess alcohol stage to the action of an excess of unreacted liquid lower fatty acid led in counter-current to them. Y

2. A process for the direct conversion of watersoluble lower fatty acids with monohydric aliphatic alcohols into highly concentrated esters which are practically free from alcohols, in which p the esterilcation is effected in two consecutive,

conjoint, but separately proceeding working stages,Y in such a manner that in the rst stage the aqueous fatty acid is esterified in the presence of a mineral acid as a catalyst, by passing downwards through a column in which rise vapors of the alcohol in excess, then as a second stage the vapor-mixture of alcohol-ester-water passing out at the head of the column is allowed to rise in a second column in the presence of a mineral acid acting as a catalyst against downwardly'moving aqueous fatty acid in excess, for practically complete esterication of the alcohol contained in the rising vapors, and finally the vapor-mixture consisting practically only of ester and water leaves the system and the ester is separated.

3. In a process as claimedin claim 2 removing a portion of the excess alcohol contained in the vapor-mixture leaving the excess alcohol stage prior to entry into the excess acid stage.

4. In a process as claimed in claim 2 removing a portion of the excess alcohol contained in the vapor-mixture leaving the excess alcohol stage prior to entry into the excess acid stageby washing with warm water at a temperature which exceeds the boiling point of the binary vapor-mixture of ester-water and of the ternary vapormixture of ester-water-alcohol formed but does not attain the boiling point of the alcohol-water solution formed.

5. Ina process as claimed in clam2 removing i a portion of the excess alcohol contained in the vapor-mixture leaving the excess alcohol stage prior to entry into the excess acid stage by washing with a dilute solution of the acid to be esteried, distilling off the alcohol from the wash liquid obtained, and returning the alcohol distilled off and the residual dilute and each one separately to the esterication process. i GBOR 'rRK. 

